The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/mm/mincore.c

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    1 /*
    2  *      linux/mm/mincore.c
    3  *
    4  * Copyright (C) 1994-2006  Linus Torvalds
    5  */
    6 
    7 /*
    8  * The mincore() system call.
    9  */
   10 #include <linux/pagemap.h>
   11 #include <linux/gfp.h>
   12 #include <linux/mm.h>
   13 #include <linux/mman.h>
   14 #include <linux/syscalls.h>
   15 #include <linux/swap.h>
   16 #include <linux/swapops.h>
   17 #include <linux/hugetlb.h>
   18 
   19 #include <asm/uaccess.h>
   20 #include <asm/pgtable.h>
   21 
   22 static void mincore_hugetlb_page_range(struct vm_area_struct *vma,
   23                                 unsigned long addr, unsigned long end,
   24                                 unsigned char *vec)
   25 {
   26 #ifdef CONFIG_HUGETLB_PAGE
   27         struct hstate *h;
   28 
   29         h = hstate_vma(vma);
   30         while (1) {
   31                 unsigned char present;
   32                 pte_t *ptep;
   33                 /*
   34                  * Huge pages are always in RAM for now, but
   35                  * theoretically it needs to be checked.
   36                  */
   37                 ptep = huge_pte_offset(current->mm,
   38                                        addr & huge_page_mask(h));
   39                 present = ptep && !huge_pte_none(huge_ptep_get(ptep));
   40                 while (1) {
   41                         *vec = present;
   42                         vec++;
   43                         addr += PAGE_SIZE;
   44                         if (addr == end)
   45                                 return;
   46                         /* check hugepage border */
   47                         if (!(addr & ~huge_page_mask(h)))
   48                                 break;
   49                 }
   50         }
   51 #else
   52         BUG();
   53 #endif
   54 }
   55 
   56 /*
   57  * Later we can get more picky about what "in core" means precisely.
   58  * For now, simply check to see if the page is in the page cache,
   59  * and is up to date; i.e. that no page-in operation would be required
   60  * at this time if an application were to map and access this page.
   61  */
   62 static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
   63 {
   64         unsigned char present = 0;
   65         struct page *page;
   66 
   67         /*
   68          * When tmpfs swaps out a page from a file, any process mapping that
   69          * file will not get a swp_entry_t in its pte, but rather it is like
   70          * any other file mapping (ie. marked !present and faulted in with
   71          * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
   72          */
   73         page = find_get_page(mapping, pgoff);
   74 #ifdef CONFIG_SWAP
   75         /* shmem/tmpfs may return swap: account for swapcache page too. */
   76         if (radix_tree_exceptional_entry(page)) {
   77                 swp_entry_t swap = radix_to_swp_entry(page);
   78                 page = find_get_page(&swapper_space, swap.val);
   79         }
   80 #endif
   81         if (page) {
   82                 present = PageUptodate(page);
   83                 page_cache_release(page);
   84         }
   85 
   86         return present;
   87 }
   88 
   89 static void mincore_unmapped_range(struct vm_area_struct *vma,
   90                                 unsigned long addr, unsigned long end,
   91                                 unsigned char *vec)
   92 {
   93         unsigned long nr = (end - addr) >> PAGE_SHIFT;
   94         int i;
   95 
   96         if (vma->vm_file) {
   97                 pgoff_t pgoff;
   98 
   99                 pgoff = linear_page_index(vma, addr);
  100                 for (i = 0; i < nr; i++, pgoff++)
  101                         vec[i] = mincore_page(vma->vm_file->f_mapping, pgoff);
  102         } else {
  103                 for (i = 0; i < nr; i++)
  104                         vec[i] = 0;
  105         }
  106 }
  107 
  108 static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  109                         unsigned long addr, unsigned long end,
  110                         unsigned char *vec)
  111 {
  112         unsigned long next;
  113         spinlock_t *ptl;
  114         pte_t *ptep;
  115 
  116         ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  117         do {
  118                 pte_t pte = *ptep;
  119                 pgoff_t pgoff;
  120 
  121                 next = addr + PAGE_SIZE;
  122                 if (pte_none(pte))
  123                         mincore_unmapped_range(vma, addr, next, vec);
  124                 else if (pte_present(pte))
  125                         *vec = 1;
  126                 else if (pte_file(pte)) {
  127                         pgoff = pte_to_pgoff(pte);
  128                         *vec = mincore_page(vma->vm_file->f_mapping, pgoff);
  129                 } else { /* pte is a swap entry */
  130                         swp_entry_t entry = pte_to_swp_entry(pte);
  131 
  132                         if (is_migration_entry(entry)) {
  133                                 /* migration entries are always uptodate */
  134                                 *vec = 1;
  135                         } else {
  136 #ifdef CONFIG_SWAP
  137                                 pgoff = entry.val;
  138                                 *vec = mincore_page(&swapper_space, pgoff);
  139 #else
  140                                 WARN_ON(1);
  141                                 *vec = 1;
  142 #endif
  143                         }
  144                 }
  145                 vec++;
  146         } while (ptep++, addr = next, addr != end);
  147         pte_unmap_unlock(ptep - 1, ptl);
  148 }
  149 
  150 static void mincore_pmd_range(struct vm_area_struct *vma, pud_t *pud,
  151                         unsigned long addr, unsigned long end,
  152                         unsigned char *vec)
  153 {
  154         unsigned long next;
  155         pmd_t *pmd;
  156 
  157         pmd = pmd_offset(pud, addr);
  158         do {
  159                 next = pmd_addr_end(addr, end);
  160                 if (pmd_trans_huge(*pmd)) {
  161                         if (mincore_huge_pmd(vma, pmd, addr, next, vec)) {
  162                                 vec += (next - addr) >> PAGE_SHIFT;
  163                                 continue;
  164                         }
  165                         /* fall through */
  166                 }
  167                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
  168                         mincore_unmapped_range(vma, addr, next, vec);
  169                 else
  170                         mincore_pte_range(vma, pmd, addr, next, vec);
  171                 vec += (next - addr) >> PAGE_SHIFT;
  172         } while (pmd++, addr = next, addr != end);
  173 }
  174 
  175 static void mincore_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
  176                         unsigned long addr, unsigned long end,
  177                         unsigned char *vec)
  178 {
  179         unsigned long next;
  180         pud_t *pud;
  181 
  182         pud = pud_offset(pgd, addr);
  183         do {
  184                 next = pud_addr_end(addr, end);
  185                 if (pud_none_or_clear_bad(pud))
  186                         mincore_unmapped_range(vma, addr, next, vec);
  187                 else
  188                         mincore_pmd_range(vma, pud, addr, next, vec);
  189                 vec += (next - addr) >> PAGE_SHIFT;
  190         } while (pud++, addr = next, addr != end);
  191 }
  192 
  193 static void mincore_page_range(struct vm_area_struct *vma,
  194                         unsigned long addr, unsigned long end,
  195                         unsigned char *vec)
  196 {
  197         unsigned long next;
  198         pgd_t *pgd;
  199 
  200         pgd = pgd_offset(vma->vm_mm, addr);
  201         do {
  202                 next = pgd_addr_end(addr, end);
  203                 if (pgd_none_or_clear_bad(pgd))
  204                         mincore_unmapped_range(vma, addr, next, vec);
  205                 else
  206                         mincore_pud_range(vma, pgd, addr, next, vec);
  207                 vec += (next - addr) >> PAGE_SHIFT;
  208         } while (pgd++, addr = next, addr != end);
  209 }
  210 
  211 /*
  212  * Do a chunk of "sys_mincore()". We've already checked
  213  * all the arguments, we hold the mmap semaphore: we should
  214  * just return the amount of info we're asked for.
  215  */
  216 static long do_mincore(unsigned long addr, unsigned long pages, unsigned char *vec)
  217 {
  218         struct vm_area_struct *vma;
  219         unsigned long end;
  220 
  221         vma = find_vma(current->mm, addr);
  222         if (!vma || addr < vma->vm_start)
  223                 return -ENOMEM;
  224 
  225         end = min(vma->vm_end, addr + (pages << PAGE_SHIFT));
  226 
  227         if (is_vm_hugetlb_page(vma)) {
  228                 mincore_hugetlb_page_range(vma, addr, end, vec);
  229                 return (end - addr) >> PAGE_SHIFT;
  230         }
  231 
  232         end = pmd_addr_end(addr, end);
  233 
  234         if (is_vm_hugetlb_page(vma))
  235                 mincore_hugetlb_page_range(vma, addr, end, vec);
  236         else
  237                 mincore_page_range(vma, addr, end, vec);
  238 
  239         return (end - addr) >> PAGE_SHIFT;
  240 }
  241 
  242 /*
  243  * The mincore(2) system call.
  244  *
  245  * mincore() returns the memory residency status of the pages in the
  246  * current process's address space specified by [addr, addr + len).
  247  * The status is returned in a vector of bytes.  The least significant
  248  * bit of each byte is 1 if the referenced page is in memory, otherwise
  249  * it is zero.
  250  *
  251  * Because the status of a page can change after mincore() checks it
  252  * but before it returns to the application, the returned vector may
  253  * contain stale information.  Only locked pages are guaranteed to
  254  * remain in memory.
  255  *
  256  * return values:
  257  *  zero    - success
  258  *  -EFAULT - vec points to an illegal address
  259  *  -EINVAL - addr is not a multiple of PAGE_CACHE_SIZE
  260  *  -ENOMEM - Addresses in the range [addr, addr + len] are
  261  *              invalid for the address space of this process, or
  262  *              specify one or more pages which are not currently
  263  *              mapped
  264  *  -EAGAIN - A kernel resource was temporarily unavailable.
  265  */
  266 SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len,
  267                 unsigned char __user *, vec)
  268 {
  269         long retval;
  270         unsigned long pages;
  271         unsigned char *tmp;
  272 
  273         /* Check the start address: needs to be page-aligned.. */
  274         if (start & ~PAGE_CACHE_MASK)
  275                 return -EINVAL;
  276 
  277         /* ..and we need to be passed a valid user-space range */
  278         if (!access_ok(VERIFY_READ, (void __user *) start, len))
  279                 return -ENOMEM;
  280 
  281         /* This also avoids any overflows on PAGE_CACHE_ALIGN */
  282         pages = len >> PAGE_SHIFT;
  283         pages += (len & ~PAGE_MASK) != 0;
  284 
  285         if (!access_ok(VERIFY_WRITE, vec, pages))
  286                 return -EFAULT;
  287 
  288         tmp = (void *) __get_free_page(GFP_USER);
  289         if (!tmp)
  290                 return -EAGAIN;
  291 
  292         retval = 0;
  293         while (pages) {
  294                 /*
  295                  * Do at most PAGE_SIZE entries per iteration, due to
  296                  * the temporary buffer size.
  297                  */
  298                 down_read(&current->mm->mmap_sem);
  299                 retval = do_mincore(start, min(pages, PAGE_SIZE), tmp);
  300                 up_read(&current->mm->mmap_sem);
  301 
  302                 if (retval <= 0)
  303                         break;
  304                 if (copy_to_user(vec, tmp, retval)) {
  305                         retval = -EFAULT;
  306                         break;
  307                 }
  308                 pages -= retval;
  309                 vec += retval;
  310                 start += retval << PAGE_SHIFT;
  311                 retval = 0;
  312         }
  313         free_page((unsigned long) tmp);
  314         return retval;
  315 }

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